1. Technical Field
Embodiments of the present invention relate to a cooling device and an image forming apparatus incorporating the cooling device.
2. Related Art
Known image forming apparatuses serve as printers, facsimile machines, copiers, and multifunctional apparatuses having two or more functions of the printers, facsimile machines, and copiers. In these image forming apparatuses, as an image forming operation proceeds, temperatures of components disposed in each process unit such as a fixing unit and a development unit provided in the image forming apparatus and temperatures of recording media such as paper sheets on which an image is formed increase.
In order to prevent the inconvenience due to an increase in temperature of any components and/or recording media beyond a permissible temperature value, it has been known that an image forming apparatus includes a cooling device to cool the heated components and/or recording media therein.
Known cooling devices have two cooling types, which are an air type cooling device and a liquid type cooling device. The air type cooling device cools a cooling target by blowing cool air. The liquid type cooling device cools a cooling target by conveying heat absorbed by a heat receiver disposed in contact with the cooling target and releases the heat via a heat releasing part. Generally, the liquid type cooling device can achieve a higher cooling effectiveness than the air type cooling device.
The following liquid type cooling device is known as an example of a cooling device to cool components provided in each process unit.
Developer that includes toner (e.g., one-component developer) or toner and carrier particles (e.g., two-component developer) contained in the development unit is susceptible to frictional heat generated when the developer is agitated and conveyed in the development unit or fixing heat generated in the fixing unit of the image forming apparatus. Due to the frictional heat and/or the fixing heat, the temperature of the toner increases to cause a toner cohesion. The toner cohesion can lead to production of a defect image.
In order to prevent such a toner cohesion, the liquid type cooling device includes a heat receiver to absorb heat of the developer indirectly from a sidewall of a developer container in which the developer is contained. By so doing, the temperature of the developer is maintained within a given range.
The following liquid type cooling device is known as a cooling device to cool recording media.
After application of heat and pressure to a recording medium in the fixing device, the recording medium is conveyed to a sheet discharging tray. As the recording medium stacks with other recording medium or media in the sheet discharging tray, the toner particle softens due to heat in the stacked recording media. Further, since the recording media are piled or stacked with each other in the sheet discharging tray, a pressure is generated due to a weight of the recording media. Accordingly, the toner can stick two adjacent recording media together. In this case, if the recording media are detached forcibly from each other, the toner image formed on both or either one of the adjacent recording media can be damaged or broken. This inconvenience is referred to as toner blocking.
In order to reduce or prevent occurrence of toner blocking, after the toner image is fixed to the recording medium or media by application of heat and pressure, the heat receiver absorbs heat from the recording media directly or indirectly to cool the recording medium or media.
For example, Japanese Patent Application Publication No. JP 2010-266810-A discloses a liquid type cooling device to cool a recording medium after the recording medium is heated to fix a toner image thereto in the fixing unit. The liquid type cooling device disclosed in JP 2010-266810-A includes a cooling roller, a radiator, and an air blowing fan. The cooling roller functions as a heat receiver to absorb heat from the recording media. The radiator functions as a heat releasing unit to release the heat absorbed by the cooling roller. The air blowing fan functions as an air blower to blow air (or wind) to the radiator for enhancing a heat releasing effect of the radiator.
In the liquid type cooling device disclosed in JP 2010-266810-A, a rotation speed of the air blowing fan is adjusted according to a type of recording media to be cooled after the toner image is fixed thereto by application of heat and pressure in the fixing unit. Accordingly, a cooling capacity of the cooling roller to cool the recording media varies.
Demands to increase types of recording media to be used for image formation in an image forming apparatus have been growing.
Typical fixing units include a fixing member such as a fixing roller and a pressure member such as a pressure roller. In such typical fixing units, the fixing member forms a fixing nip contact area together with the pressure member, and is controlled to have a substantially constant temperature when the recording medium is fixed in the fixing unit by application of heat and pressure. Therefore, when a subsequent recording medium having a paper type different from the preceding recording medium passes through the fixing nip contact area, a heat capacity and conductivity of the subsequent recording medium change from the preceding recording medium. Therefore, a required heat amount for the subsequent recording medium changes, and the temperature of a heat member such as a heater to heat the fixing member varies to maintain the substantially constant temperature of the fixing member. Accordingly, when the temperature of the heating member varies, not only the heat amount for the subsequent recording medium but also the heat amount to be released from the fixing unit into an apparatus body of the image forming apparatus changes.
Therefore, in order to encourage energy efficiency, it is preferable that the cooling device incorporated in the image forming apparatus for various types of recording media having different heat amounts for image fixing by application of heat and pressure.
The liquid type cooling device disclosed in JP 2010-266810-A can cool a recording medium according to the type of the recording medium, and therefore can vary the cooling capacity accordingly.
However, due to the following reasons, installation space for the radiator and air blowing fan(s) cannot be more flexible, and therefore it is not likely to decrease a size of the image forming apparatus and to achieve better cooling efficiency for a cooling target.
A fan casing of typical air blowing fans used in the image forming apparatus has a substantially square shape in vertical cross section in a rotation shaft of fans of the air blowing fan, that is, in an air blowing direction of the air blowing fan. Due to cost performance and versatility, many typical radiators have a rectangular shape in vertical cross section in a direction that air generated by the air blowing fan hits and passes through the radiators.
The liquid type cooling device disclosed in JP 2010-266810-A has one air blowing fan to be rotated with respect to one radiator. Even though not shown in JP 2010-266810-A in detail, from FIGS. 3 and 5 of JP 2010-266810-A, the shapes of the radiator and the air blowing fan may have similar shapes to the above-described typical radiators and the air blowing fans having the substantially square shapes in vertical cross section in the air blowing direction of the air blowing fan.
For these reasons, even if vacant space in the image forming apparatus has a rectangular shape in vertical cross section in the air blowing direction of the air blowing fan and can obtain a desired heat releasing effect when air hits the radiator at a given speed, the installation space has no other choice to have a substantially square shape for the radiator and the air blowing fan. Therefore, the entire area of the rectangular shape in vertical cross section of the vacant space in the image forming apparatus cannot be utilized effectively.